This was a recycled desktop in service, working very well.. until one day, it stopped..

Went from Amber (10 seconds) to flash 2,3,2,3,2,3,2,3.

Best information online identified it as a RAM issue. Unfortunately, reseating ram did nothing.

Pulled CPU cooler to check heat sink material. Difficult to remove and very dry. fixed, still broken

Found a hint about CPU Battery, replaced and fixed it.

Seems like it was stuck in a secure reboot mode.. not sure how.. but this worked for me.